Based on previous threads I've seen on Chemistry Community, people generally advise to take Chem 14B before taking Chem 14BL. There's no rule, but it may make your workload and studying a bit easier to manage!

Most people take Chem 14BL in a quarter after they have taken Chem 14B, so they are more familiar with the material. Chem 14BL is also work heavy, so you should keep that in mind when choosing classes.